.github: Add needs build for generate-test-matrix (#70456)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/70456
This job was still running on workflows despite ciflow not being enabled
This makes it so that test matrix generation only occurs before tests
are actually run.
Signed-off-by: Eli Uriegas <eliuriegas@fb.com>
Test Plan: Imported from OSS
Reviewed By: atalman
Differential Revision: D33338946
Pulled By: seemethere
fbshipit-source-id: 4b83d5fe6572771807708764609a72c4f1c5745d
